Objective To investigate the effects of quercetin and X-ray on collagen synthesis of cultured human keloid-derived fibroblast and the mechanism.Methods Collagen synthesis of cultured human keloid and normal fibroblasts were detected by hydroxyproline colorimetric analysis. Immunocytochemical staining was used to investigate collagen I and III expression. mRNA expression of collagen I and III

and transforming growth factor （TGF）-β1 were assayed by reverse transcription-polymerase chain reaction （RT-PCR） and real-time PCR. Results Quercetin inhibited the collagen synthesis of both keloid and normal fibroblasts in a dose-dependent manner. Immunocytochemical staining indicated that collagen I and III were down-regulated by quercetin and X-ray （P<0.05）

particularly collagen I （P<0.05）. mRNA expression of both collagen I and III in quercetin groups significantly decreased compared with that in control group （P<0.05）

especially in the group treated with both quercetin and X-ray （P<0.01）. mRNA level of TGF-β1 gene was down-regulated by quercertin （P<0.05）. Conclusions Quercetin will probably be one of the new medicines which could effectively treat keloid. Quercetin combined with X-ray could reduce the dose of radiation.